Application

Feeder Refill from Pneumatic Conveying

Answer in brief

Refill a loss-in-weight feeder from a vacuum receiver mounted above it: level sensors trigger a defined charge, the discharge valve isolates conveying vacuum from the weighed hopper, and the conveying cycle rebuilds the buffer while the feeder returns to gravimetric control. Fast, repeatable, gentle refills within a narrow level band are what keep the feeder's accuracy claim true in production.

Reviewed August 14, 2026 · Updated August 14, 2026

The problem

A loss-in-weight feeder cannot weigh while it is being filled, and a pneumatic conveying system cannot deliver material instantaneously. Left uncoordinated, the two systems collide: refills arrive late and the feeder runs empty, or they arrive violently and aerate the powder, upset the weight signal and change the density the volumetric bridge depends on. The interface between conveying receiver and feeder hopper is where continuous processes quietly lose their accuracy.

Desired outcome

Refills should be fast, repeatable and gentle: triggered by hopper level, completed within a narrow band, with conveying air fully disengaged from the weighing system. The feeder controller should bridge each refill with learned behavior and return to gravimetric control within seconds, so that downstream the mass flow never visibly stumbles.

Process approach

A vacuum receiver sits above the feeder with a buffer volume matched to the feed rate. When the hopper level reaches the refill point, the receiver discharge valve opens and drops a defined charge into the feeder hopper; the conveying cycle then rebuilds the buffer while the feeder returns to gravimetric control. Filters keep conveying air out of the process, discharge valves isolate conveying vacuum from the weighed hopper, and level sensors define a narrow refill band so density stays predictable. For fragile or blend-sensitive products, dense-phase conveying variants reduce velocity into the receiver.

Selection factors

Refill charge size and frequency versus feeder hopper working volume. Vacuum versus pressure conveying, and dilute versus dense phase for the material. Discharge valve type that seals conveying vacuum away from the weighing system. Venting of displaced air during the drop, without fluidizing the hopper contents. Level measurement and the refill band that keeps bulk density repeatable. Control integration: refill triggering, feed-forward and the volumetric bridge. Cleaning and changeover requirements across recipes.

Common failure modes

Refill charges too large for the hopper band, so density and the volumetric bridge drift.
Conveying vacuum reaches the weighed hopper and corrupts the load-cell signal.
The receiver empties into a still-dosing feeder in one violent, aerating drop.
Buffer volume too small, so the conveying system cannot keep up at peak rates.
Displaced air during the drop has no vent path and blows dust into the room.
Filter cleaning pulses shake the structure during fine dosing.

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Frequently asked questions

Why does refill design decide loss-in-weight accuracy?

Because the feeder is blind during every refill: it doses volumetrically on learned behavior until the weight signal stabilizes. Slow, irregular or aerating refills stretch that blind window and change the density the bridge assumes — which is where accuracy is actually lost.

How big should the vacuum receiver above a feeder be?

Large enough to hold at least one full refill charge plus the material conveyed during a cycle, small enough that product does not sit and segregate. The working rule: the receiver refills the feeder in seconds, and the conveying system refills the receiver in the pauses.

How is conveying vacuum kept away from the weighing system?

With a discharge valve that seals the receiver from the feeder hopper except during the drop, and venting that lets displaced air escape without a pressure path into the weighed volume. Vacuum reaching the load cells reads as phantom weight change.

Does dense phase conveying help with feeder refill?

For fragile, abrasive or blend-sensitive products, yes: lower velocities reduce breakage, segregation and aeration in the receiver, so the refill drops denser, calmer material — exactly what the volumetric bridge wants.

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